Method of insulating an electrical conductor

ABSTRACT

High density, high dielectric strength, wood pulp fiber paper is provided with a surface coating of a lubricant which produces a hard, dry, slippery film on the paper, thereby preventing breaking of the paper as it is wrapped around electrical conductors.

United States Patent 1191 1111 3,874,961 Steinert Apr. 1, 1975 [54]METHOD OF INSULATING AN 2,164,168 6/1939 Wertzheiser (it al. 174/120 CELECTRICAL CONDUCTOR 2,298,748 10/1942 Bt'O WI'I 156/56 2,389,72511/1945 GllllS et a1 156/54 175 Inventor: T or W- Stemert. e o M2,5s0,050 12/1951 Sparks et'al..... 156/53 2,697,675 12 1954 G 156 289[73] Assgnee K'mberly'clark corporat'on 2,786,757 3i1957 423/331 Neenahi3,112,357 ll/l963 11111101,... 156/53 3,207,603 9/1965 Savit 117/154[22] Filed Sept 1972 3,284,279 11/1966 Rumberger 117/152 [21] Appl. No.2288,820

Related Application Data Primary Examiner-Char1es E. Van Horn [60]Continuation of Scr. No. 22,102, March 5, 1970, Assistant i1J L iabandoned, which is a division of Ser. No. 644,093, Anome, Agent or FirmBreitenfeld & Levine June 7, 1967, abandoned.

152] US. Cl 156/53, 156/192, 156/289,

174/110 P, 174/120 C, 174/121 B [57] ABSTRACT [51] Int. Cl. H011) 3/52,H01b 13/08 1 1 Field 01 Search- 56, High density, high dielectricstrength, wood pulp fiber 174/1 10 121 122 120 paper is provided with asurface coating ofa lubricant 423/327, 331 which produces a hard, dry,slippery film on the paper, thereby preventing breaking of the paper asit is 1561 Refere Ce C te wrapped around electrical conductors.

UNITED STATES PATENTS 2,029,546 2/1936 Schatzcl 174/122 5 Claims, N0Drawings METHOD OF INSULATING AN ELECTRICAL CONDUCTOR This applicationis a continuation of copending application Ser. No. 22,102, filed Mar.5, 1970, which was a division of copending application Ser. No. 644,093,filed June 7, 1967, both now abandoned.

This invention relates to a method of insulating wires which carryelectric current.

Electric wire is, in practice, provided with a paper insulation wrappingin various ways, depending in part on the ultimate use to which the wireis put. For example, the insulated wire may be wound on a core in themanufacture of a transformer. In large power transformers, theinsulation on each wire or conductor becomes all or part of theinsulation between the turns of the windings. To aid in understandingthis invention, reference will be made to its use in connection with themanufacture of electrical transformers. However, the invention obviouslyhas broader scope and its usefulness is not limited to this particularenvironment.

Insulation of transformer wire is accomplished by drawing the wirethrough the center of a series of revolving taping heads. Continuouswebs of paper are drawn from supply rolls of the paper mounted on thetaping heads, the webs being fed over adjustable guides and finallywrapped in spiral fashion around the wire. Since a number of tapingheads are employed, several layers of paper are applied to the wire, thelayers being overlapped or butted to create a smooth surface. Theinsulated, or taped, conductors are subsequently wound around a core toproduce the transformer.

For many years, paper made from used rope (Manila hemp) has beenemployed to insulate many types of electrical conductors, includingthose employed in the manufacture of transformers. Such paper is strongand stretchable, and these mechanical qualities permit the paper to beused on high speed taping machines without breaking. However, rope fiberpaper has a low dielectric strength, and consequently the insulationthickness of the conductors must be relatively large.

It would be desirable, therefore, to employ high dielectric strengthpaper to insulate some types of electrical conductors. High dielectricstrength paper, such as is conventionally employed in electricalcapacitors, is more dense than rope fiber paper. Therefore, a smalleramount of thinner high dielectric strength paper could replace thethicker rope fiber paper, thus reducing the overall bulk of atransformer. High dielectric strength paper is made from wood pulpfibers, and in the past, attempts to use such paper to insulate wireshave not been successful. If the taping machine is run at normal speeds,the wood pulp paper breaks. Addition of plasticizers to the paper, toincrease its stretchiness, has not solved the problem. If the tapingmachine is run more slowly, the wood pulp paper can be used withoutbreaking, but the speeds are so slow as to be uneconomical.

It is an object of the present invention to provide a method ofinsulating electrical conductors with a high density, high dielectricstrength, wood pulp paper capable of being used without breaking onconventional wire insulating equipment while the latter operates atnormal speed, i.e., a speed comparable to that employed when insulatingwith rope fiber paper.

These objects are achieved, according to the present invention byproviding high dielectric strength, wood fiber, paper with a surfacecoating of a lubricant. The surface lubrication apparently reduces thefriction between the paper and the various metal surfaces over which itis drawn during the taping, or wire wrapping, process, and also reducesthe friction between the layers of paper wrapped around the conductor.Paper lubricated according to the present invention, as well asidentical paper without lubrication, have been used on several types ofinsulating machines which differ markedly in their mode of operation,and the surface lubrication has been found to be essential tosatisfactory performance in all cases. For example, on one tapingmachine, having a normal taping speed of 35 feet per minute, paperwithout surface lubrication was found to break when the speed of themachine reached 22 feet per minute. In contrast, when lubricated paperaccording to this invention was employed, the machine taped successfullyat 40 feet per minute.

Lubricants which have been found to work satisfactorily include refinedparaffin wax, a zirconium wax complex, an ethylene oxide polymer, thealkali metal or alkaline earth soaps of stearic acid, a complexcolloidal magnesium aluminum silicate product derived from anaturally-occurring mineral and sold by R. T. Vanderbilt Company, Inc.under the trademark Biltcote. Other materials believed useful for papersurface lubrication are unsaponified stearic acid, and other solid fattyacids or their soaps, and the vegetable waxes such as carnauba wax. Onthe other hand, products which have been tried unsuccessfully includetalc and lubricating oils. It appears, therefore, that the lubricantused must be one which forms a hard, dry, slippery film on the papersurface.

The lubricant, as either a dispersion or a solution in an organicsolvent or water, may be applied to the paper in any appropriate manner,such as by a simple roll coating technique. It has been found that aslittle as 0.001 pounds of lubricant per 1,000 square feet of treatedpaper surface yields successful results.

A laboratory test for determining the efficacy of any particular surfacelubrication treatment is defined by ASTM D 202 which measures thesurface friction of paper. According to this procedure, a sheet of paperis secured to an inclined plane, the angle of inclination of the planebeing adjustable. Another sheet of the same paper is secured to aweighted block placed on the plane with the paper sheets in contact. Theangle of inclination of the plane with respect to the horizontal,measured in degrees, at which the block slides freely on the plane is anindication of the relative slipperiness of the paper. In general, highdensity, high dielectric strength, wood pulp paper without treatmentaccording to this invention, has been found to give angle-ofinclinationreadings of about 20 30. In contrast, the same paper after surfacelubrication treatment gives readings of 10- 15.

Some specific examples of paper treatment according to this inventionare set forth below:

EXAMPLE I A paper made from unbleached kraft softwood pulp, the paperhaving a thickness of 2 mils, a density of 1.0 grams per cubiccentimeter, and a dielectric strength of 600 volts per mil, was treatedwith an aqueous dispersion of a refined paraffin wax having a meltingpoint of 134F, and dried. The amount of wax applied to the sheet was0.01 pounds per thousand square feet of sheet surface treated. The paperwas treated by conventional size press application, without the surfacetreatment with wax, the paper had a surface friction angle of 27, asmeasured in accordance with ASTM D-202. After application of the surfacelubricant, the friction angle was reduced to 8.

EXAMPLE II Instead of paraffin wax, the paper of Example I was treatedwith an aqueous dispersion of a zirconium-wax complex (a commercialwater repellant treatment for textiles and paper, sold under thetrademark Sunchem F H by Sun Chemical Company) and dried. The amount ofthis material applied was 0.003 pounds per thousand square feet of sheetsurface. This treatment reduced the surface friction angle to 10.

EXAMPLE III Instead of paraffin wax, the paper of Example I was treatedwith an aqueous solution of an ethylene oxide polymer (sold under thetrademark Polyox WSR 301 by Union Carbide Corporation). The amount ofdry polymer deposited was 0.005 pounds per thousand.

square feet of sheet surface. The surface friction angle was reduced to14 by this treatment.

EXAMPLE IV Instead of paraffin wax, the paper of Example I was treatedwith an aqueous dispersion of calcium stearate and dried. The amount ofcalcium stearate applied was 0.025 pounds per thousand square feet ofsheet surface. The surface friction angle was reduced to 7.

EXAMPLE V EXAMPLE VI Instead of paraffin wax, the paper of Example I wastreated with an aqueous solution of sodium stearate and dried. Theamount of dry material deposited was 0.01 pounds per thousand squarefeet of sheet surface. The surface friction angle was reduced to 13.

EXAMPLE VII Another proprietary wax complex water repellant sizingmaterial (sold under the trademark Nalan HR by E. I. duPont de Nemours &Co., Inc.) was substituted for the product (Sunchem FH) used in Example11. The amount of dry product applied was 0.003 pounds per thousandsquare feet of sheet surface. The surface friction angle was reduced to10.

EXAMPLE VIII Example VII was repeated with the level of treatmentreduced to 0.0015 pounds per thousand square feet of sheet surface. Thesurface friction angle of the treated paper was 14.

EXAMPLE IX A paper made from unbleached kraft softwood pulp, the paperhaving a thickness of 2 mils, a density of 0.8 grams per cubiccentimeter, and a dielectric strength of 425 volts per mil, was treatedwith an aqueous dispersion of a refined paraffin wax having a meltingpoint of 134F, and dried. The amount of wax applied to the sheet was0.007 pounds per thousand square feet of sheet surface treated. Withoutthe surface treatment, the paper had a surface friction angle of 24.After application of the surface lubricant, the friction angle wasreduced to 9.

EXAMPLE X A paper made from unbleached kraft softwood pulp, the paperhaving a thickness of 2 mils, a density of 1.0 grams per cubiccentimeter, and a dielectric strength of 600 volts per mil, was treatedwith an aqueous dispersion of a refined paraffin wax having a meltingpoint of 134F. and dried. The amount of lubricant applied was 0.007pounds per thousand square feet of sheet surface treated. The paper wasthen supercalendered to a density of 1.1 grams per cubic centimeter. Thefinal product had a surface friction angle of 7 and a dielectricstrength of 725 volts per mil.

It will be noted that the paper employed in the present invention iswood pulp paper having a high dry dielectric strength exceeding 400volts per mil. Equally important, the paper has a high density of atleast 0.80

high density, the paper provides increased dielectric strength whenimpregnated with insulating liquids. For example, the kraft pulp paperdescribed in Example I, after lubrication and impregnation withtransformer oil had an impulse voltage breakdown strength of 4500 voltsper mil. On the other hand, rope fiber paper having a density of onlyabout 0.70 grams per cubic centimeter had an impulse voltage breakdownstrength of about 2200 volts per mil after impregnation with transformeroil.

The paper may be treated according to this invention on only one side,where in use only one side of the paper frictionally contacts parts ofthe taping or wrapping machine. l-Iowever, in some circumstances, it maybe necessary or desirable to treat both sides of the pa per. In anycase, the values given herein concerning the amount of lubricant appliedto the paper relate to the amount applied to each treated surface of thepaper.

It may be pointed out that although the primary benefit of the presentinvention involves the solution of the problem of paper breaking duringthe taping of conductors, the invention also plays a part in the windingof the taped conductors. When the conductors were wrapped in wood pulppaper without surface lubrication treatment, it was difficult toproperly position them on the core around which they are wound. Thisproblem was, however, alleviated by the use of surface lubrication onthe paper.

The invention has been shown and described in preferred form only, andby way of example, and many variations may be made in the inventionwhich will still be comprised within its spirit. It is understood,therefore, that the invention is not limited to any specific form orembodiment except insofar as such limitations are included in theappended claims.

What is claimed is:

1. A method of insulating an electrical conductor comprising the stepsof lubricating the surface of a paper web with a lubricant which forms ahard, dry, slippery film on the paper, the lubricant being applied tothe paper in an amount between 0.001 and 0.025

6 pounds per thousand square feet of web surface, and cant is anethylene oxide polymer. after said hard dry film has formed, wrappingthe web 4. A method as defined in claim 1 wherein the lubriaround theconductor. cant is a soap of stearic acid.

2. A method as defined in claim 1 wherein the lubri- 5. A method asdefined in claim 1 wherein the lubricant is a wax. 5 cant is a magnesiumaluminum silicate complex.

3. A method as defined in claim 1 wherein the lubri-

1. A METHOD OF INSULATING AN ELECTRICAL CONDUCTOR COMPRISING THE STEPS OF LUBRICATING THE SURFACE OF A PAPER WEB WITH A LUBRICANT WHICH FORMS A HARD, DRY, SLIPPERY FILM ON THE PAPER, THE LUBRICANT BEING APPLIED TO THE PAPER IN AN AMOUNT BETWEEN 0.001 AND 0.025 POUNDS PER THOUSAND SQUARE FEET OF WEB SURFACE, AND AFTER SAID HARD DRY FILM HAS FORMED, WRAPPING THE WEB AROUND THE CONDUCTOR.
 2. A method as defined in claim 1 wherein the lubricant is a wax.
 3. A method as defined in claim 1 wherein the lubricant is an ethylene oxide polymer.
 4. A method as defined in claim 1 wherein the lubricant is a soap of stearic acid.
 5. A method as defined in claim 1 wherein the lubricant is a magnesium aluminum silicate complex. 